Mobile bearing glenoid prosthesis

ABSTRACT

A prosthesis assembly configured for use with a scapula in one embodiment includes a spherical humeral component, an elongated glenoid bearing including a first bearing surface with (i) a first spherical end portion with a first radius of curvature, (ii) a second spherical end portion with a second radius of curvature, and (iii) a central portion located between the first spherical end portion and the second spherical end portion, and a first coupling portion extending from a second bearing surface opposite the bearing surface, and a base configured to rotatably support the elongated glenoid bearing, wherein the first radius of curvature is substantially equal to the second radius of curvature and the central portion does not have a radius of curvature that is substantially equal to the second radius of curvature.

This application is a utility application claiming priority to U.S.provisional application No. 61/331,458, filed May 5, 2010, entitled“Mobile Bearing Glenoid Prosthesis,” the disclosure of which isincorporated by reference herein in its entirety.

BACKGROUND

The present disclosure relates generally to shoulder prostheses, andmore particularly to shoulder prostheses configured for use in shouldershaving glenoid vault erosion or defects.

A typical shoulder or glenohumeral joint is formed in a human body wherethe humerus 10 movably contacts the scapula 12 as shown in FIG. 1. Thescapula 12 includes a glenoid fossa 14 that forms a socket against whichthe head of the humerus 10 articulates. At this socket, the scapula 12includes cartilage 16 that facilitates such articulation. Beneath thecartilage is subchondral bone 18 that forms a wall of a glenoid vault 20that defines a cavity which contains cancellous bone 22. The subchondralbone 18 that forms the glenoid vault 20 defines a glenoid rim 21 at aperiphery of the glenoid vault that is attached to the cartilage 16 (seeFIG. 1). During the lifetime of a patient, the glenoid fossa 14 maybecome worn, especially at its posterior and/or superior portionsthereby causing severe shoulder pain and limiting the range of motion ofthe patient's shoulder joint. To alleviate such pain and increase thepatient's range of motion, a shoulder arthroplasty may be performed.

Shoulder arthroplasty often involves surgical replacement of the glenoidfossa with a conventional glenoid prosthesis such as the one disclosedin U.S. Pat. No. 6,911,047, the disclosure of which is hereinincorporated by reference. The glenoid prosthesis, when implanted,provides a new laterally-facing bearing surface, which may be concave orconvex, for articulation with a complementary bearing surface of anatural or prosthetic humeral head. Such conventional glenoid prosthesisis typically formed from UHMW polyethylene, titanium, or cobalt chromeand includes bone anchor(s) such as peg(s), screw(s), post(s), or a keelextending from a back side of the device opposite its bearing surface.So configured, the back side of the prosthesis is typically securedagainst subchondral bone of the glenoid vault while the bone anchor(s)may extend into the cavity of the glenoid vault whereby it may becomeanchored to cancellous bone located within the glenoid vault.

Shoulder prostheses such as those described above are very effective.During typical movement of the shoulder joint after arthroplasty,however, the humeral head rotates and slides against the glenoidsurface. Glenoid components, however, are typically spherical in shape.Accordingly, the translation of the humeral head in the shoulder jointafter arthroplasty can result in edge loading of the prosthesisassembly. Edge loading can result in limited motion, instability, andaccelerated wear.

Some attempts have been made to reduce the problems associated with edgeloading. Some prosthesis assemblies introduce a mismatch in the diameterof the head and the diameter of the glenoid component. This approachaccommodates translation of the humeral head but does not eliminate edgeloading. Additionally, the resulting loss of optimal coverage of thehumeral head results in increased instability. Another approach that hasbeen used is to use varying diameters in the glenoid component. Thisapproach also fails to eliminate edge loading and further results inreduced stability.

What is needed therefore is an improved prosthesis assembly for use inpatients requiring shoulder arthroplasty. An improved prosthesisassembly which reduces edge loading without increasing instability ofthe shoulder joint is also needed.

SUMMARY

In accordance with one embodiment of the present disclosure, there isprovided a prosthesis assembly configured for use with a scapula whichincludes a spherical humeral component, an elongated glenoid bearingincluding a first bearing surface with (i) a first spherical end portionwith a first radius of curvature, (ii) a second spherical end portionwith a second radius of curvature, and (iii) a central portion locatedbetween the first spherical end portion and the second spherical endportion, and a first coupling portion extending from a second bearingsurface opposite the bearing surface, and a base configured to rotatablysupport the elongated glenoid bearing, wherein the first radius ofcurvature is substantially equal to the second radius of curvature andthe central portion does not have a radius of curvature that issubstantially equal to the second radius of curvature.

Pursuant to another embodiment of the present disclosure, a prosthesisassembly configured for use with a scapula includes a spherical humeralcomponent, a stretched glenoid bearing including a first bearing surfacewith (i) a first spherical outer portion with a first radius ofcurvature, (ii) a second spherical outer portion with a second radius ofcurvature, and (iii) a central portion located between the firstspherical outer portion and the second spherical outer portion, and afirst mating portion extending from a second bearing surface oppositethe first bearing surface, and a base including a third bearing surfaceand a second mating portion extending from the third bearing surface,the base configured to rotatably support the stretched glenoid bearing,wherein the first radius of curvature is substantially equal to thesecond radius of curvature and the central portion does not have aradius of curvature that is substantially equal to the second radius ofcurvature.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a cross-sectional view of an anatomically normalglenohumeral joint of a human patient;

FIG. 2 depicts a perspective view of a shoulder prosthesis assembly ofthe present disclosure;

FIG. 3 depicts an end cross-sectional view of the glenoid bearing baseof FIG. 2;

FIG. 4 depicts a side cross-sectional view of the glenoid bearing baseof FIG. 2;

FIG. 5 depicts a top plan view of the base of FIG. 2;

FIG. 6 depicts a perspective view of the glenoid bearing of FIG. 2;

FIG. 6A depicts a cross sectional view of a spherical humeral componentthat may be used with the glenoid bearing of FIG. 6;

FIG. 7 depicts an end plan view of the glenoid bearing of FIG. 6;

FIG. 8 depicts a side cross-sectional view of the glenoid bearing ofFIG. 6;

FIG. 9 depicts a top perspective view of a shoulder assembly prosthesiswith a stretched bearing component that does not include a rimreplacement vault;

FIG. 10 depicts a bottom perspective view of the shoulder assemblyprosthesis of FIG. 9;

FIG. 11 depicts a top plan view of the shoulder assembly prosthesis ofFIG. 9;

FIG. 12 depicts a cross-sectional view of the shoulder assemblyprosthesis;

FIG. 13 depicts a cross-sectional view of a shoulder assembly prosthesiswith a stretched bearing component which is snap-fit to a basecomponent;

FIG. 14 depicts a partial cross-sectional view of the mating recess ofthe base component of FIG. 13; and

FIG. 15 depicts a partial plan view of the mating portion of thestretched bearing component of FIG. 13.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

While the shoulder prosthesis assembly described herein is susceptibleto various modifications and alternative forms, specific embodimentsthereof have been shown by way of example in the drawings and willherein be described in detail. It should be understood, however, thatthere is no intent to limit the shoulder prosthesis assembly to theparticular forms disclosed, but on the contrary, the intention is tocover all modifications, equivalents, and alternatives falling withinthe spirit and scope of the invention as defined by the appended claims.

Referring now to FIG. 2, there is shown a shoulder prosthesis assembly100 that is configured to be implanted in a human scapula. Theprosthesis assembly 100 includes a glenoid base component 102 and aglenoid bearing 104. The glenoid base component 102 in this embodimentis made entirely of a metallic material, while the glenoid bearing 104is made entirely of a polymeric material. Preferably, the glenoid basecomponent 102 is made of a biological grade stainless steel or titaniummaterial. Also, the glenoid bearing support may include a porous-coatingon its entire outer surface to facilitate biological ingrowth of apatient's bone. The glenoid bearing 104 is preferably made entirely of apolymer such as polyethylene. One particular polyethylene that is wellsuited for use as the bearing component is a high molecular weightpolyethylene, for example, ultra-high molecular weight polyethylene(UHMWPE).

The glenoid base component 102 is described with further reference toFIGS. 3 and 4. In particular, the glenoid base component 102 includes aglenoid vault-occupying portion 106 and a glenoid rim replacementportion 108. The glenoid rim replacement portion 108 is attached to theglenoid vault-occupying portion 106 as shown in FIGS. 3-4. If desired,the glenoid rim replacement portion 108 and the glenoid vault-occupyingportion 106 may be attached to each other by being integrally formedtogether as a single part.

Alternatively, the glenoid rim replacement portion 108 and the glenoidvault-occupying portion 106 may be separately formed. In suchembodiments, a cavity may be formed in the glenoid vault-occupyingportion 106 which receives a complementary shaped cavity occupyingportion of the glenoid rim replacement portion 108. If desired, theseparately formed glenoid rim replacement portion 108 and glenoidvault-occupying portion 106 may be attached to each other by snap-fit orfriction-fit features or the like. One such friction fit feature is aball taper connection which allows for version correction of the glenoidrim replacement portion 108 independent of the version of the glenoidvault-occupying portion 106. Alternatively, soft tissue may be reliedupon to maintain the glenoid rim replacement portion 108 mated with theglenoid vault-occupying portion 106.

The glenoid vault-occupying portion 106 is configured to occupy at leasta portion of the glenoid vault of a scapula, such as the glenoid vault20 shown in FIG. 1. If desired, the glenoid vault-occupying portion 106may configured to substantially completely fill the glenoid vault of ascapula, such as glenoid vault 20 shown in FIG. 1. The glenoidvault-occupying portion 106 has an exterior wall 110 and an exteriorwall 112 as best shown in FIG. 3. When the glenoid vault-occupyingportion 106 is viewed in cross-section (see FIG. 3) the exterior wall110 and the exterior wall 112 are positioned with respect to each otherto define a generally V-shaped wedge 114.

The glenoid vault-occupying portion 106 has a mating portion 120 whichextends inwardly from a bearing surface 122. The bearing surface 122provides support for the glenoid rim replacement portion 108 and may bepolished to reduce generation of wear products. The mating portion 120includes a wall portion 124 which defines a generally cone shaped innerperiphery of the base 102. A ridge 126 and a ridge 128 extend into therecess formed by the wall portion 124. The ridges 126 and 128 extendpartially along the inner periphery defined by the wall portion 124.

A rim 130 extends from the bearing surface 122. The rim 130 and wedge114 define a pocket 132 which extends completely about the wedge 114. Ifdesired, bone graft material may be placed into the pocket 132.

The glenoid vault-occupying portion 106 further includes fastenerchannels 134 and 136. Fasteners may be inserted through the matingrecess 120 and through the channels 134 and 136 to affix the glenoidbase component 102 to a glenoid.

The glenoid bearing 104 is shown in more detail in FIGS. 6-8. Inparticular, the bearing 104 includes a body 140 and a mating member 142.The body 140 includes a bearing surface 144 configured to articulatewith a spherical humerus component, such as the spherical humeralcomponent 30 shown in FIG. 6A with a glenoid component 32, and a bearingsurface 145 configured to articulate with the bearing surface 122.

The glenoid bearing 104 is a stretched bearing. A “stretched bearing” isa bearing that includes a bearing surface with at least three distinctgeometries. With reference to FIG. 8, the bearing surface 144 includesan outer bearing portion 146, a central bearing portion 148, and anouter bearing portion 150. The outer bearing portion 146 is sphericallyshaped with a radius of curvature 152 and the outer bearing portion 150is spherically shaped with a radius of curvature 154. The radius ofcurvature 152 is preferably the same length as the radius of curvature154. The central portion 148, however, has a radius of curvature 156that is much larger than the radius of curvature 152 and the radius ofcurvature 154. In some embodiments, the central portion 148 includes asubstantially planar portion. A rim 158 extends completely around thebearing surface 144.

The mating member 142 includes a wall 160 that defines a conical outerperiphery and slots 162 and 164. The slots 162 and 164 extend inwardlyfrom the outer periphery defined by the wall 160 and are configured toreceive the ridges 126 and 128, respectively. The slot 162 includes twoend portions 166 and the slot 164 includes two end portions 168. Thelength of the slots 162 and 164 about the outer periphery defined by thewall 160 is greater than the length of the ridges 126 and 128 about theinner periphery defined by the wall portion 124. The conical shapedefined by the wall 160 is complementary to the conical shape defined bythe wall portion 124.

The shoulder prosthesis assembly 100 is assembled by implanting theglenoid base component 102 in the glenoid vault 20 of a patient. Ifdesired, fasteners may be inserted through the mating recess 120 and thechannels 134 and 136 to affix the base component 102 to the glenoidvault. A glenoid bearing 104 is then selected. The glenoid bearing 104is selected such that the outer bearing portions 146 and 150 have radiiof curvatures 152 and 154 which provide the desired coverage for thediameter of the spherical humeral head that is used. Accordingly, anumber of different glenoid bearings 104 may be provided in a kit with anumber of different radii of curvature 152 and 154.

The selected glenoid bearing 104 is then coupled with the implanted basecomponent 102 by axially aligning the slots 162 and 164 with the ridges126 and 128 and inserting the mating member 142 into the mating recess120. As the mating member 142 is inserted, the mating member 142contacts the ridges 126 and 128 and the mating member 142 is slightlycompressed until the slots 162 and 164 are vertically aligned with theridges 126 and 128 at which point the mating member 142 decompressesthereby locking the bearing 104 within the mating recess 120. In deviceswith different radii of curvature 152 and 154, the vertical height ofthe ridges 126 and 128 may be offset, with a similar offset in thevertical height of the slots 162 and 164 to ensure a desired orientationof the bearing 104 on the base component 102.

Once the bearing 104 is locked with the base 102, the bearing surface145 is rotatably supported on the bearing surface 122. Rotation of thebearing 104 on the base 102 is provided since the length of the slots162 and 164 about the outer periphery defined by the wall 160 is greaterthan the length of the ridges 126 and 128 about the inner peripherydefined by the wall portion 124. Rotation is limited by contact of theend portions 166 with the ridge 126 and contact of the end portions 168with the ridge 128. The extent of rotation may be adjusted by providingslots of differing lengths. By joining the slots, 360 degree rotationmay be allowed.

Rotation is effected when the shoulder prosthesis assembly 100 isimplanted as the spherical humeral head contacts the ridge 158. At thecentral portion 148, the curvature of the rim does not complement thecurvature of the spherical head. Accordingly, a torque is generated onthe bearing 104. The torque causes the bearing 104 to rotate. As thebearing 104 rotates, the spherical head continues to contact the rim 158until the spherical head moves into one of the outer bearing portions146 or 150. The radius of curvature of the rim 158 in the outer bearingportions 146 and 150 matches the radii of curvature 152 and 154 in theouter portions 146 and 150. Thus, since the radii of curvature 152 and154 complement the radius of curvature of the spherical head, thespherical head is captured at the outer portions 146 or 150.

In the embodiment of FIG. 2, rotation of the bearing 104 on the base 102is limited to less than 360 degrees. Accordingly, the bearing surface122 need not be circular. Rather, an hour-glass shaped bearing surfacemay be used to provide rotational support throughout rotation of thebearing 104. Use of a circular bearing surface 122, however, allows asurgeon to use either limited rotation bearings 104 or bearings 104 thatcan rotate 360 degrees with a single base 102, reducing the number ofbases needed in inventory.

Another benefit of a circular bearing surface on a base component can berealized with bases using a conical stem in place of the wedge 114.Specifically, site preparation is simplified for base componentsincorporating stems and circular bearing surfaces. A guide wire may beused to guide a rotating bone cutting device with multiple cutting edgessuch that the glenoid vault is shaped to receive the stem and circularbearing surface in a single operation. If desired, fins may be providedon the stem in such base components to prevent rotation of the basecomponent.

In embodiments of the shoulder prosthesis assembly 100 allowing 360degree rotation, the ridges 126 and 128 and the slots 162 and 164 may beomitted. The vertical height of the mating member 142 and the pressureprovided by soft tissue around the shoulder joint are sufficient tomaintain the mating member 142 within the mating recess 120. Inembodiments incorporating the ridges 126 and 128 and the slots 162 and164, the vertical height of the mating member 142 may be reduced toprovide a truncated cone since the slot/ridge locking mechanism and thepressure provided by soft tissue around the shoulder joint aresufficient to maintain the mating member 142 within the mating recess120.

While the embodiment of FIGS. 2-8 incorporates a rim replacement vault,various modifications may be made within the scope of the invention. Byway of example, FIGS. 9-12 depict a shoulder prosthesis assembly 200that is configured to be implanted in a vault of a human scapula. Theprosthesis assembly 200 includes a glenoid base component 202 and aglenoid bearing 204. The glenoid base component 202 in this embodimentis made entirely of a metallic material, while the glenoid bearing 204is made entirely of a polymeric material. Preferably, the glenoid basecomponent 202 is made of a biological grade stainless steel or titaniummaterial. Also, the glenoid bearing support may include a porous-coatingon its entire outer surface to facilitate biological ingrowth of apatient's bone. The glenoid bearing 204 is preferably made entirely of apolymer such as polyethylene. One particular polyethylene that is wellsuited for use as the bearing component is a high molecular weightpolyethylene, for example, ultra-high molecular weight polyethylene(UHMWPE).

The glenoid base component 202 includes a stem 206 and a base plateportion 208. If desired, the stem 206 and the base plate portion 208 maybe attached to each other rather than being integrally formed togetheras a single part. The stem 206 is configured to occupy at least aportion of the glenoid vault of a scapula, such as the glenoid vault 20shown in FIG. 1.

The base component 202 has a mating recess 220 which extends inwardlyfrom a bearing surface 222. The bearing surface 222 provides support forthe bearing 204 and may be polished to reduce generation of wearproducts. The base component 202 further includes a number of fins 224which prevent rotation of the base component 202 once the base component202 is implanted.

The glenoid bearing 204 includes a body 240 and a mating member 242. Themating member 242 is shaped complementary to the conical shape of thecoupling member 220. The body 240 includes a bearing surface 244configured to articulate with a spherical humerus component (not shown)and a bearing surface 245 configured to articulate with the bearingsurface 222.

The glenoid bearing 204 is a stretched bearing which includes an outerbearing portion 246, a central bearing portion 248, and an outer bearingportion 250. The outer bearing portions 246 and 250 are sphericallyshaped, preferably with a similar radius of curvature. The centralportion 248, however, has a radius of curvature that is much larger thanthe radius of curvature of the bearing portions 246 and 250. In someembodiments, the central portion 248 includes a substantially planarportion. A ridge 258 extends completely about the periphery of thecentral bearing portion 248.

The shoulder prosthesis assembly 200 is assembled and operated insubstantially the same manner as the shoulder prosthesis assembly 200.One difference is that the glenoid bearing 204 is not rotatably lockedto the base component 202. Rather, the pressure provided by soft tissuearound the shoulder joint is sufficient to maintain the mating member242 within the mating recess 220.

Rather than relying solely upon pressure provided by soft tissue, vaultversions may incorporate friction fit or snap-fit features to maintainthe bearing component mated with the base component. By way of example,FIGS. 13-15 depict a shoulder prosthesis assembly 300 that includes aglenoid base component 302 and a stretched glenoid bearing 304.

The base component 302 includes a mating recess 306 with a conicalportion 308, a neck 310 and a bulbous void 312. The stretched glenoidbearing 304 includes a mating portion 314 with a conical portion 316, aneck 318 and a bulbous portion 320. The conical portion 316, the neck318 and the bulbous portion 320 are sized complementary to the conicalportion 308, the neck 310 and the bulbous void 312, respectively. Thebulbous portion 320, however, has a diameter in a plane orthogonal tothe longitudinal axis 322 of the mating portion 306 that is smaller thanthe diameter of the neck 310 in the plane in which the narrowest portionof the neck 310 lies. Accordingly, the bulbous portion 320 must becompressed somewhat in order to slide the bulbous portion 320 past theneck 310 along the longitudinal axis 324 of the mating portion 306 andinto the bulbous void 312. In some embodiments, a void may be formedwithin the bulbous portion 320 to facilitate compression of the bulbousportion 320.

There is a plurality of advantages arising from the various features ofeach of the embodiments of the shoulder prosthesis assembly describedherein. It will be noted that alternative embodiments of the shoulderprosthesis assembly may not include all of the features described yetstill benefit from at least some of the advantages of such features.Those of ordinary skill in the art may readily devise their ownimplementations of the shoulder prosthesis assembly that incorporatesone or more of the features and fall within the spirit and scope of thepresent invention as defined by the appended claims.

What is claimed is:
 1. A prosthesis assembly configured for use with ascapula, comprising: a spherical humeral component; a stretched glenoidbearing including a first bearing surface with (i) a first sphericalouter portion with a first radius of curvature, (ii) a second sphericalouter portion with a second radius of curvature, (iii) a central portionlocated between the first spherical outer portion and the secondspherical outer portion, said central portion including a substantiallyflat portion, and (iv) a first mating portion extending from a secondbearing surface opposite the first bearing surface and including a firstlocking component; and a base configured to rotatably support thestretched glenoid bearing, the base including a second mating portionconfigured to receive the first mating portion and including a secondlocking component, wherein the first radius of curvature issubstantially equal to the second radius of curvature and the centralportion does not have a radius of curvature that is substantially equalto the second radius of curvature, and the first locking component andthe second locking component are configured such then when the firstlocking component and the second locking component are engaged, thefirst and second locking components limit (i) axial movement of thefirst mating portion with respect to the second mating portion, and (ii)rotation of the stretched glenoid bearing to less than 360 degrees. 2.The prosthesis assembly of claim 1, wherein the base comprises: aglenoid vault-occupying portion configured to occupy at least a portionof a cavity in a glenoid vault, the glenoid vault-occupying portionincluding an outer wall; and a rim, wherein the rim and the outer walldefine a pocket.
 3. The prosthesis assembly of claim 2, wherein: thefirst mating portion includes a third locking component; and the secondmating portion includes a fourth locking component configured torotatably couple with the third locking component.
 4. The prosthesisassembly of claim 1, wherein: the first bearing surface includes anon-circular outer periphery.
 5. The prosthesis assembly of claim 4,wherein: the base includes a non-circular outer periphery; and thesecond mating portion includes a circular periphery.
 6. The prosthesisassembly of claim 1, wherein: the first locking component extends aboutan outer periphery of the first mating portion; the second lockingcomponent extends about an inner periphery of the second mating portion;and the length of the first locking component about the outer peripheryis less than the length of the second locking component about the innerperiphery.
 7. A prosthesis assembly configured for use with a scapula,comprising: a spherical humeral component; a stretched glenoid bearingincluding a first bearing surface with (i) a first spherical outerportion with a first radius of curvature, (ii) a second spherical outerportion with a second radius of curvature, (iii) a central portionlocated between the first spherical outer portion and the secondspherical outer portion, said central portion including a substantiallyflat portion, and (iv) a first mating portion extending from a secondbearing surface opposite the first bearing surface and including a firstlocking component; and a base including (i) a third bearing surface, and(ii) a second mating portion extending from the third bearing surfaceand including a second locking component, the base configured torotatably support the stretched glenoid bearing, wherein the centralportion includes a radius of curvature that is not substantially equalto the first radius of curvature or the second radius of curvature, andthe first locking component and the second locking component areconfigured such then when the first locking component and the secondlocking component are engaged, the first and second locking componentslimit (i) axial movement of the first mating portion with respect to thesecond mating portion, and (ii) rotation of the stretched glenoidbearing to less than 360 degrees.
 8. The prosthesis assembly of claim 7,wherein: the first mating portion is substantially conical; and thesecond mating portion is configured to receive the first mating portion.9. The prosthesis assembly of claim 8, wherein a periphery of the thirdbearing surface is generally oval.
 10. The prosthesis assembly of claim8, wherein the base comprises: a bone contacting surface on a side ofthe base opposite to the third bearing surface; and a stem extendingoutwardly from the bone contacting surface.
 11. The prosthesis assemblyof claim 10 wherein the base is metallic, the base further comprising:at least one fin extending outwardly from the stem.
 12. The prosthesisassembly of claim 8, wherein: the first mating portion includes a thirdlocking component; and the second mating portion includes a fourthlocking component configured to rotatably couple with the third lockingcomponent.
 13. The prosthesis assembly of claim 12, wherein: the firstlocking component extends about an outer periphery of the first matingportion; and the second locking component extends about an innerperiphery of the second mating portion.
 14. The prosthesis assembly ofclaim 13, wherein: the length of the first locking component about theouter periphery is less than the length of the second locking componentabout the inner periphery.
 15. The prosthesis assembly of claim 7,wherein the first radius of curvature is substantially equal to thesecond radius of curvature.